Several different kinds of polarizing film are available for polarizing unpolarized light. Absorbing (dichroic) polarizers have, as an inclusion phase, polarization-dependent absorbing species, often an iodine-containing chain, that are aligned within a polymer matrix. Such a film absorbs light polarized with its electric field vector aligned parallel to absorbing species and transmits light polarized perpendicular to the absorbing species. Another type of polarizing film is a reflective polarizer, which separates light in different polarization states by transmitting light in one state and reflecting light in the other state. One type of reflective polarizer is a multilayer optical film (MOF), which is formed of a stack of many layers of alternating polymer materials. One of the materials is optically isotropic while the other is birefringent, with one of its refractive indices matched to that of the isotropic material. Light incident in one polarization state experiences the matched refractive indices and is substantially specularly transmitted through the polarizer. Light incident in the other polarization state, however, experiences multiple coherent or incoherent reflections at the interfaces between the different layers and is reflected by the polarizer.
Another type of reflective polarizing film is constructed from inclusions dispersed within a continuous phase matrix. The inclusions are small relative to the width and height of the film. The characteristics of these inclusions can be manipulated to provide a range of reflective and transmissive properties to the film. The inclusions constitute a disperse polymer phase within the continuous phase matrix. The inclusion size and alignment can be altered by stretching the film. Either the continuous phase or the disperse phase is birefringent, with one of the refractive indices of the birefringent material matching to the refractive index of the other phase, which is optically isotropic. Selection of the materials for the continuous and disperse phases, along with the degree of stretching, can affect the degree of birefringent refractive index mismatch between the disperse phase and the continuous phase. Other characteristics can be adjusted to improve the optical performance.